Oct 20th: The Adrenal Glands and the Pancreas

What are the four layers of the adrenal gland, from surface to centre?

Zona glomerulosa, zona fasciculata, zona reticularis, and the medulla.

Which layers make up the cortex, and what class of molecules do they produce?

The zona glomerulosa, fasciculata, and reticularis. They produce steroids.

What does the medulla produce

Amines (catecholamines).

Which hormone class does the zona glomerulosa make?

Mineralocorticoids (salt).

What is the main hormone of the zona glomerulosa?

Aldosterone

What triggers release from the zona glomerulosa?

Angiotensin II and high blood potassium

Which hormone class does the zona fasciculata make

Glucocorticoids (sugar).

What is the main hormone of the zona fasciculata?

Cortisol

What triggers release from the zona fasciculata?

ACTH

Which hormone class does the zona reticularis make?

Androgens (sex steroids).

What is the main hormone of the zona reticularis?

Adrenal androgens.

What triggers release from the zona reticularis?

ACTH

Which hormone class does the medulla make?

Catecholamines (stress)

What is the main hormone of the medulla?

Epinephrine

What triggers release from the medulla?

Sympathetic nerves.

What three inputs stimulate the hypothalamus to start the cortisol pathway?

Stress, low blood glucose, and time of day.

What does the hypothalamus release, and what is its effect?

CRH, which stimulates (+) the anterior pituitary.

What does the anterior pituitary release, and what is its effect?

ACTH, which stimulates (+) the adrenal cortex (zona fasciculata).

Which part of the adrenal gland makes cortisol?

The adrenal cortex, specifically the zona fasciculata.

How is cortisol secretion regulated once cortisol levels rise?

Negative feedback. Cortisol feeds back (-) to reduce signalling in the pathway.

When is plasma cortisol concentration highest?

6 am, when you wake

Why does it matter that cortisol is highest when you wake?

It helps release fuel for the day ahead.

What does stress do to the cortisol rhythm?

Stress adds peaks on top of the daily rhythm.

What body parts does cortisol act on?

Cortisol acts on almost every tissue.

What does cortisol do to muscle?

It increases protein breakdown (proteins → amino acids).

What does cortisol do to adipose tissue?

It increases lipolysis (triglycerides → glycerol and fatty acids).

What does cortisol do in the liver?

It increases gluconeogenesis (new glucose made from amino acids and glycerol).

What does cortisol do to the immune system?

It decreases inflammation, so immune responses are suppressed.

What does cortisol do to bone?

It decreases bone formation, so less calcium is kept in bone.

What is the net effect of cortisol across these tissues?

Blood glucose rises and fuel stays available through prolonged stress or fasting.

Where does cortisol’s new glucose come from?

The liver makes it through gluconeogenesis, using amino acids from muscle protein and glycerol from adipose triglycerides.

What does muscle protein supply to the liver?

Amino acids

What do adipose triglycerides supply to the liver?

Glycerol

What does the liver do with the glycerol and amino acids

Gluconeogenesis, producing new glucose

Where does the glucose go after the liver makes it?

Into the blood, and then to the brain.

What happens to the fatty acids released from adipose triglycerides?

They are burned by muscle instead of glucose, sparing glucose for the brain.

What is Cushing syndrome

Too much cortisol for too long.

What most often causes Cushing syndrome?

Long-term glucocorticoid medication.

What is Cushing’s disease?

A pituitary tumour releasing too much ACTH.

What cortisol action explains high blood glucose (hyperglycemia) in Cushing syndrome?

Increased gluconeogenesis in the liver.

What cortisol action explains muscle wasting and weakness?

Increased muscle protein breakdown

What cortisol action explains thin skin, easy bruising, and stretch marks?

Increased protein breakdown in skin.

What cortisol action explains osteoporosis and slowed growth in children?

Decreased bone formation.

What cortisol action explains frequent infections?

Immune suppression.

What cortisol action explains a round face and fat on the abdomen and upper back?

Fat stores are redistributed to the trunk and face.

Is ACTH high in a patient that has their antierior pit. tumour releasing ACTH?

ACTH is high

Is ACTH high in a patient that has their Adrenal cortex releasing cortisol?

ACTH is low

What kind of hormone is aldosterone, and how does it act?

A steroid hormone. It crosses the cell membrane and binds a receptor inside kidney tubule cells.

What does the aldosterone receptor do once bound?

It switches on genes for sodium channels and sodium-potassium pumps.

Why does aldosterone’s effect take hours to develop?

It works by switching on genes, rather than acting immediately.

What triggers aldosterone release?

Low blood pressure or volume (via angiotensin II), and high blood potassium.

Which layer of the adrenal gland releases aldosterone?

The zona glomerulosa.

What does aldosterone do in the kidney tubule?

Sodium reabsorption increases (↑) and potassium excretion increases (↑).

What happens to water after sodium is reabsorbed?

Water follows the sodium by osmosis, so blood volume increases (↑).

What is the final response of the pathway?

Blood pressure increases (↑) toward the set point.

How is the pathway shut off?

Negative feedback (−). Restored pressure removes the trigger.

What triggers epinephrine release?

Sympathetic nerves (fight-or-flight).

What is the relationship between cortisol and epinephrine?

Epinephrine and cortisol are two stress hormones that act on two different time scales.

Where does epineph. come from? Where does cortisol come from?

Epinephrine: adrenal medulla. Cortisol: adrenal cortex (zona fasciculata).

What triggers epineph. and cortisol hormone?

Epinephrine: sympathetic nerves. Cortisol: ACTH from the anterior pituitary.

What is the chemical type of epinephrine and cortisol?

Epinephrine: hydrophilic amine. Cortisol: lipophilic steroid.

Where are the receptors for epinephrine and cortisol?

Epinephrine: on the cell membrane. Cortisol: inside the cell, where it changes gene expression.

What are the onset and duration of epinephrine and cortisol?

: Epinephrine: seconds, short-lived. Cortisol: minutes to hours, long-lasting.

How do epinephrine and cortisol raise blood glucose?

Epinephrine: by glycogen breakdown. Cortisol: by gluconeogenesis.

What situations are epinephrine and cortisol best suited to?

Epinephrine: sudden danger. Cortisol: prolonged stress or fasting.

Why does receptor location explain the difference in speed between epinephrine and cortisol?

Epinephrine binds a membrane receptor, so it acts in seconds. Cortisol must enter the cell and change gene expression, so it takes minutes to hours

What percentage of the pancreas is exocrine?

98%

What do the exocrine cells of the pancreas release, and where does it go?

Acinar cells release digestive enzymes into ducts that lead to the small intestine.

What percentage of the pancreas is endocrine?

About 1 to 2%.

What do the endocrine cells of the pancreas release, and where does it go?

Islets of Langerhans release hormones directly into the blood.

Which cells in the islets release insulin?

Beta (β) cells, the most numerous.

Which cells in the islets release glucagon?

Alpha (α) cells.

Which cells in the islets release somatostatin?

Delta (δ) cells.

What is the role of somatostatin?

It acts as a local brake on both insulin and glucagon.

Which islet cell type is the most numerous?

Beta cells.

What is the difference between how exocrine and endocrine pancreatic secretions travel?

Exocrine secretions (digestive enzymes) travel through ducts to the small intestine. Endocrine secretions (hormones) go directly into the blood.

(Fasted state) What happens first?

Blood glucose falls.

(Fasted state) Which cells respond when blood glucose falls, and what do they release?

Alpha cells release glucagon.

(Fasted state) What does the liver do in response to glucagon?

It breaks down glycogen and makes new glucose.

(Fasted state) What does the liver do with the glucose it makes?

: It releases the glucose into the blood.

(Fasted state) What is the final result of the pathway?

Blood glucose rises toward the set point.

(Fed state) What happens first?

Blood glucose rises.

(Fed state) Which cells respond when blood glucose rises, and what do they release?

Beta cells release insulin.

(Fed state) What does insulin signal muscle and adipose to do?

Take up glucose.

(Fed state) What does insulin signal the liver to do?

Store glucose as glycogen.

(Fed state) Where does glucose go when it leaves the blood?

: It is used for ATP or stored.

(Fed state) What is the final result of the pathway?

Blood glucose falls toward the set point.

(Both states) How do glucagon and insulin differ in their effect on blood glucose?

Glucagon raises blood glucose (fasted state). Insulin lowers blood glucose (fed state).

What happens after meals to bring blood glucose back to the set point?

• Blood glucose rises

• beta cells release insulin, muscle and adipose take up glucose, and the liver stores glycogen

• Blood glucose then falls back toward the set point.

(Fasted state) What happens between meals to bring blood glucose back to the set point?

Blood glucose falls, alpha cells release glucagon, and the liver breaks down glycogen and makes new glucose.

Blood glucose then rises back toward the set point.

What are two ways the insulin loop fails?

Type 1 and type 2 diabetes are two ways the insulin loop fails.

What is the basic problem in type 1 diabetes?

The immune system destroys the beta cells.

What is the basic problem in type 2 diabetes?

Muscle, adipose, and liver respond poorly to insulin.

How much insulin is released in type 1 diabetes? How much insulin is released in type 2 diabetes?

T1: little to none

T2: Normal or high at first, then it falls as beta cells tire.

How do target tissues respond to insulin in type 1 diabetes?

Normally

How do target tissues respond to insulin in type 2 diabetes?

The response is reduced (insulin resistance).

What is the typical onset of type 1 diabetes?

Often in childhood or young adulthood, and it is sudden.

What is the typical onset of type 2 diabetes?

Usually in adulthood, and it is gradual over years.

What share of all diabetes cases is type 1, and what share is type 2?

Type 1: about 5 to 10%. Type 2: about 90 to 95%.

What are the main risk factors for type 1 diabetes?

Inherited susceptibility plus an immune trigger.